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52 The PCB Design Magazine • May 2015 in various prepreg styles. Typical resin content ranges are as follows For 85N polyimide on E-Glass Style 106 68–72%, Style 1080 55–65% Style 2313 50–55%, Style 2116 50%, Style 7628 35–40% For 92ML on E-Glass Style 104 90%, Style 106 90%, Style 1080 84% For Multiclad ® HF on E-Glass Style 104 88–90%, Style 106 86–89%, Style 1080 80–83% Style 2313 78%, Style 2116 78% For 85NT on Nonwoven Aramid (for constant CTE values regardless of buildup) All styles 49% For 25FR on E-Glass (for constant Dk values regardless of buildup) All styles 73% One final note: Dielectric constant values for 85N, 85NT and 92ML are given at 1 MHz, while Multiclad HF is given at 10 GHz. The values for frequencies greater than 1 MHz can be estimated based on the 1 MHz value using a mathematical model. Actual test results (see graph, below) conform well to the model and indicates that for most materials, dielectric con- stant shifts lower with increasing frequency. The basic math looks like this: Where Dk o = dielectric constant at frequency f o Dk i = dielectric constant at frequency f i df o = loss tangent at f o If Dk =3.6 at 1 MHz with df = 0.014, then Dk at 1 GHz = 3.6*[10 9 /10 6 ] ((-2*0.014)/ π) = 3.385 Figure 2. article THE COMPOSITE PROPERTIES OF RIGID VS. MuLTILAyER PCBS continues